Hi Have you ever tried to actually *buy* a crystal built to a specification? There is a tolerance on them. That has a profound impact on what you can *buy*.
Bob > On Jun 4, 2017, at 12:56 AM, Donald E. Pauly <trojancow...@gmail.com> wrote: > > You have a fundamental misunderstanding of the AT curve family. See > my QBASIC plot at > http://gonascent.com/papers/hp/hp5061/photos/newxtl.jpg . The > commonly described AT cut is shown as the largest sine wave in the > blue rectangle. The left side of the rectangle is -55°C, the center > is 25° C and the right side is 105° C. The bottom of the rectangle is > -16 ppm and the top is +16 ppm. > > Main Cut > Temp Freq > -55° C -16 ppm > -15° C +16 ppm > +25° C ±0 ppm > +65° C -16 ppm > 105° C +16 ppm > > You can get a lower turnover point of 24° C and an upper turnover > point of 26° C. Their amplitude would be °±0.250 ppb. As the turnover > points approach each other, their amplitude approaches zero. The line > joining all the turnover points is y= -8·x^3. The zero temperature > for 25° is y=4·x^3. Practical tolerance these days is on the order of > 0.1 minutes of arc. This is within the width of the traces in the > graph. > > You are way off on your 0° to 50° C crystal. > > ["Umm …. errr … it’s quite easy to get a +/- 2 ppm 0-50C AT cut > *including* the tolerance on the cut angle."] > > Temp Freq > 0° C -0.488 ppb (lower limit) > 12.5° C +0.488 ppb (lower turning point) > 25° C ±0 > 37.5° C -0.488 ppb (upper turning point) > 50° C +0.488 ppb (upper limit) > > As I claimed, a Thermal Electric Cooler has never been used to build a > crystal oscillator. In the 50s, TEC efficiencies were on the order of > 1% and were useless. The Soviets made coolers more practical in the > 70s with better materials. I saw one used at Telemation that was able > to measure dew point by condensing water vapor on a mirror. It looks > like efficiencies have now improved to 33% or so. > > It was only in the early 70s that Analog Devices invented the AD590 > solid state temperature sensor. It made thermister bridges obsolete. > Switching amplifiers are required to drive thermal coolers if you want > to preserve efficiency. > > πθ°μΩω±√·Γλ > WB0KVV > > ---------- Forwarded message ---------- > From: Bob kb8tq <kb...@n1k.org> > Date: Fri, Jun 2, 2017 at 12:22 PM > Subject: Re: HP5061B Versus HP5071 Cesium Line Frequencies > To: "Donald E. Pauly" <trojancow...@gmail.com> > Cc: "rwa...@aol.com" <rwa...@aol.com>, time-nuts <time-nuts@febo.com> > > Hi > > Any real crystal you buy will have a tolerance on the angle. In the > case of a crystal cut for turn the temperature will be a bit different > and you will match your oven to it. If you attempt a zero angle cut, > you will never really hit it and there is no way to compensate for the > problem. > > Bob > > On Jun 2, 2017, at 3:19 PM, Donald E. Pauly <trojancow...@gmail.com> wrote: > > A cut at that angle has no turn over temperature. The zero temperature > coefficient point is 25°. Its temperature coefficient everywhere else > is positive. > > On Friday, June 2, 2017, Bob kb8tq <kb...@n1k.org> wrote: >> >> Hi >> >> If you are going to use an oven, it’s better to run it at the turn >> temperature of >> the crystal. That would put you above 50C for an AT and a bit higher still >> for an SC. >> >> Bob > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.